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Full text of "Handbook Of Chemical Engineering - I"

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CHEMICAL ENGINEERING
T (minutes) = 300 X 2 = 600 hr. Average capacity per hour = 120,000 -T- 600 = 200 ton.
Assume average load = two-thirds full load. Required capacity per hour = 200 -f- % — 300 ton.
Assume bridge speed = 400 ft. per minute, Average bridge travel (loaded) per trip = % X 240 = 160 ft. Travel per trip (loaded and empty) = 160 X 2 = 320 ft.
Duration of bridge travel per trip = 320 •*- 400 = 0.80 min Assume average dumping time =                       1.00
Loading time =                       1.20
3.00 Assume trolley speed = 120 ft. per minute,
average trolley travel per trip = 50 ft.
Time required for trolley travel per trip = 50 -f- 120 = 0.42 min. (NOTE: Time required is less than that of bridge travel, so may be ignored.) Disregarding hoisting time, 20 trips (60 -f- 3) per hour could be made.    In which case, K = 300 -r 20 = 15 ton.
HS (hoisting speed) for 15-ton, medium-speed, crane (first speed) = 29 ft. per minute (Table 5).
Maximum lift = 40 ft., requiring 1% min. (40 -5- 29) 1.20 -f- 0.5 X 0.80 = 1.60 min. available. This does not allow sufficient margin, so try K = 20.
300 ton (required capacity per hour) -*- 20 = 15 trips per hour required.    Allows 4 min. per trip.
HS for 20-ton, medium-speed, crane (first speed) = 24 ft. per minute.
Maximum lift = 40 ft., requiring 1.66 min. (40 •?• 24) More than 2.00 min. available.
Select 20-ton crane, medium speed; hoisting speed (first), 24 ft. per minute; trolley speed, 120 ft. per minute; bridge speed, 400 ft. per minute. As average load is taken as two-thirds full load, Q" =20 ton.
Power requirements:
20 X 24
Hoisting motor = —r~— = 30 hp.                                                (5a)
Trolley motor     = 20 ^Q12Q = 6—say 10 hp.                                   (56)
Bridge motor      . gO + 0.08 X 60)400 , fl 2o5
Total....................................................  80 hp.
Initial Cost—Take cost of 5-ton, medium-speed, 25-ft. span, crane = $5,000. Cost of 20-ton, medium-speed, 50-ft. span, crane = 5,000 X 1.98 = 9,900—say $10,000 (Table 6).